The structure, function, and mechanism of the monosaccharide transport system of the human erythrocyte will be elucidated at the molecular level. The investigation of structure will include analysis of amino acid composition, determination of the molecular weight and subunit structure, delineation of the folding of the polypeptide chain relative to the plane of the membrane, labeling of the active sites for monosaccharides and cytochalasin B, and amino acid sequence determination. Aspects of function that will be examined are transport activity upon incorporation into phospholipid vesicles and the effect of lipid structure upon transport activity. The study of the mechanism of action of the purified transport system will be directed toward establishing the kinetic mechanism through an examination of transient processes. Individual steps will be recognized, and the value of rate and equilibrium constants for them will be obtained.